Current statistics state that more than 26,000 people are killed or wounded by landmines every year. Approximately one death or injury occurs every twenty minutes. Presently, it is estimated that there are more than 100 million antipersonnel or antitank mines in more then seventy countries. Already, 11 million mines have been cleared from Egypt alone. However, over 308,800 square miles of mined land still exists in Sudan alone. The impact of this proliferation of mines is clear—in Afghanistan, three hundred to three hundred sixty people are killed by mines each month. In Cambodia, one out of every 236 people is a landmine amputee. With the current technology and efforts, all existing mines may not be cleared before the year of 2100.
Landmines are generally more prevalent in under-developed countries; countries which often do not possess the financial means to afford most landmine detection devices. Indeed, the cost to purchase and install a landmine is between $3 and $30 per device, while the cost to detect and remove a single landmine is between $300 and $1,000. More effective and less costly landmine detection and removal systems are needed now perhaps more than ever—in 1994, 200,000 landmines were removed, while 2 million new mines were planted.
The ease of detecting landmines is decreasing, due to two main factors. First, newer mines contain less metal and are often much smaller, thereby becoming more difficult to detect with existing and inexpensive technology. The size of newer antipersonnel mines range from 6 to 15 cm in diameter. Therefore, detection devices must be extremely accurate in locating the mines. The lack of metal in the landmine eliminates the efficacy of current, affordable detection devices, namely metal detectors. Second, older landmines have often been in place for extended periods-often so long that any visual indication of its planting has disappeared and vegetation has grown over its surface.
The existence of vegetation over older landmines presents additional problems, including the fact that such vegetation often causes distortion of present detection techniques, since such techniques cannot be practiced immediately above the soil surface.
Present methods of detecting landmines include using metal detectors, ground penetrating radar (GPR), infrared sensors (IR), dynamic thermography (DT), and ultra-sound (US). Each of these techniques has both benefits and drawbacks.
The drawbacks of metal detectors have been previously discussed. Essentially, more and more modern mines are being manufactured with little or no metal. For example, the PMN mine, previously manufactured by the Soviet Union, is enclosed in a thick rubber casing, thereby preventing most metal detecting devices from sensing its presence.
Ground penetrating radar (GPR) is a type of detection method that actively emits electromagnetic waves and collects reflected signals. The differences in the reflected signals may indicate where landmine may be buried. GPR may be limited by environmental conditions. For example, differences in humidity in soil may result in varying readings, often indicating a landmine when none actually exists. Further, ideal conditions for detecting landmines require not only dry, consistent soil, but also the use of a low frequency signal. Unfortunately, low frequency signals provide poor resolution images in determining where such landmines may be.
Standard Infrared (IR) detection devices, also referred to as thermal radiation detection devices, typically use electromagnetic, temporal waves to radiate the soil from a stationary platform. Things beneath the surface, such as landmines, are heated through the IR radiation and the temporal signature heated landmines produce. These signatures are generally not sufficient to detect single landmines. IR detection devices that move (i.e., are not stationary) generally need to use spatial electromagnetic waves. Spatial waves may provide better resolution than temporal waves. Infrared detection devices have been known to operate either passively or actively. Passive infrared sensors detect changes in temperature based upon the natural radiation of an object, often because of changing environmental (i.e., weather) conditions. Drawbacks of known passive infrared detection techniques include the slight disparity in temperature that generally occurs through the day between a landmine and the ambient soil it is buried in. Further, results may be greatly skewed by environmental conditions (i.e., a cool wind blowing over warm soil may disrupt readings). Active infrared detection devices utilize infrared radiation to heat bodies in a wall or another medium in order to artificially stimulate their thermal signature to be detected by IR cameras. Active infrared detectors also have drawbacks, including cost, size, and weight.
Ultrasound (US) detection devices generally emit a high frequency sound (above the audible range) and collect reflections of this sound. A difference between US and GPR methods is that GPR does not cause any physical effects, while US does. As the US sound wave propagates through a medium, the sound wave causes molecules of the medium to oscillate around their equilibrium position. If the medium is entirely homogenous, i.e., no landmines, the US wave will continue propagating. If a different medium is encountered, the US wave is generally reflected and refracted. Thus, when US waves are reflected and refracted back to sensors, it is an indication of a possible landmine location. The main drawback of US detection devices is that US waves tend to greatly attenuate when the medium is air. US detection devices work best when there is little to no air gap between the emitter and the desired medium, i.e., the soil. As it is often difficult and unsafe to have a US detection device in direct contact with the soil, the results of such devices may be somewhat unreliable, due to this distance.
It has also been found that ultrasound and audible sound waves may be used to determine where landmines may be located. These waves may be transmitted toward the surface to be tested, and the reflected waves collected and analyzed. Studies have shown that when the sound waves encounter a landmine or similar foreign body, they are reflected back at a different rate than waves reflected due to normal soil conditions. By analyzing this data and comparing the differential in reflection rates, possible landmine locations may be ascertained. The device for digitally recording the reflected sound waves from a directional high sensitivity microphone is referred to herein as an “acoustic camera” for simplicity.
There are further drawbacks associated with each of the discussed detection devices. Generally, their costs are prohibitive, especially to the under-developed countries that most have the need for them. Further, the majority of devices require direct human operation, thereby placing lives in jeopardy.
Thus, there is a need for a more reliable, effective, inexpensive, and/or remotely operated landmine detection device. There is further a need for landmine detection device that may operate near enough to the surface to be tested to provide accurate readings, but for safety reasons avoids contacting the surface to be tested.
Additional advantages of embodiments of the invention are set forth, in part, in the description that follows and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention.